This invention relates to flat resistance wire or ribbon material as used in electric heating coils for cigar lighters and ignitor plugs, and more particularly to a high production method and apparatus by which ribbed or grooved strips are made, suitable for the manufacture of spiral heating coils characterized by nestable convolutions.
For quite a number of years, the heating coils of electric cigar lighters as used in automobiles were wound of flat, ribbon-like resistance wire into a spiral coil shape, utilizing an arbor and related fixtures, in a relatively slow speed process involving appreciable hand labor and handling. As so produced, the heating elements were somewhat costly and in many cases lacked uniformity, being not of especially high quality. Such heating elements were utilized with 6-volt electrical systems of automobiles, for the most part. When automobile electrical systems were improved by changing to 12-volt batteries it became necessary to use a greater length of thinner resistance-wire ribbon in the cigar lighters so as to accommodate these to the higher voltage. In so doing, the spiral-wound heating elements were found to be much less sturdy and rugged, and many instances occured where the coil convolutions became deformed, rendering the cigar lighter inoperative.
In order to remedy this condition, efforts were made to produce spiral-wound heating coils where a ribbed or angular cross-sectional configuration was imparted to the ribbon, so as to cause nesting of adjoining convolutions of the spiral coil and provide greater rigidity and mutual support. This resulted in an improved, sturdier and more rugged coil, and eliminated to a great extent the prior coil failures and burn-outs. The ribbing of the ribbon was done by placing previously cut lengths in a flat die of a press, and applying a punch to the ribbon to form the groove-like configuration. This particular procedure was not only lengthy and costly, but it also produced a high percentage of rejects. Thus, while a solution to one problem was had, there arose other problems which tended to detract from the advantages of forming the ribbon.